Disc brake caliper assembly

ABSTRACT

A disc brake caliper assembly for a rotary disc brake of a vehicle which has a wear adjustment mechanism is provided. The disc brake caliper assembly (10) includes a caliper housing (14) with a piston (28) slidably mounted therein, but prevented from rotating by a lug (30) on a brake shoe (16) secured thereto which keys in a groove (32) in the piston. An actuator screw (44) and actuator nut (66) are positioned in an internal bore (65) in the piston for mechanical actuation of the brakes. If the brake pads (20, 22) wear, on hydraulic actuation of the brakes, a thrust washer (70) engages and moves the actuator nut axially along the actuator screw to a new position which restricts reverse movement of the piston to a new (wear adjusted) position relative to the caliper housing. An actuator cone (68) having a friction clutch surface biased into engagement with a friction clutch surface on the piston prevents reverse movement of the actuator nut.

This invention relates to a disc brake caliper assembly for a rotarydisc brake of a vehicle, and in particular to a disc brake caliperassembly having a wear adjustment mechanism.

A disc brake caliper assembly having a wear adjustment mechanism isknown from GB Patent No. 1,297,495.

It is an object of the present invention to provide an improvement tothe above mentioned known arrangements.

To this end, one embodiment of a disc brake caliper assembly inaccordance with the present invention comprises first and second brakeshoes having integral brake pads of friction lining material forfrictionally engaging opposite sides of the rotary disc brake, the firstbrake shoe having a lug projecting therefrom on the opposite side to thebrake pad; a caliper housing having a cavity therein defining anexpansion chamber for hydraulic fluid; an inlet port opening into theexpansion chamber for passage of the hydraulic fluid; a piston sealinglyslidably mounted in the cavity in the caliper housing and projectingfrom one end of the cavity, the first brake shoe being secured to thepiston at one end thereof outside the cavity with the lug on the firstbrake shoe projecting into a corresponding groove in the piston to keythe first brake shoe and the piston together to prevent the pistonrotating relative to the caliper housing, the piston having an internalbore having a longitudinal axis and having an open end opening into theexpansion chamber; a thrust washer secured in the internal bore of thepiston; an actuator nut positioned in the internal bore with afunctional gap between an edge portion of the actuator nut and thethrust washer, the actuator nut having a longitudinal axis; an actuatorscrew mounted in the cavity in the caliper housing and projecting fromthe other end of the cavity, the actuator screw having a longitudinalaxis, the longitudinal axes of the actuator screw, the actuator nut, andthe internal bore being aligned, the actuator screw extending into theinternal bore and threadingly engaging the actuator nut; and actuatormeans positioned in the internal bore of the piston and engaging theactuator nut, the actuator means having a friction clutch surfacenormally resiliently biased by resilient means into engagement with acorresponding friction clutch surface in the internal bore of the pistonand directed towards the open end thereof, being rotatable relative tothe piston on disengagement of the friction clutch surfaces, and beingrotatably fixed relative to the actuator nut but axially movablerelative thereto; hydraulic actuation of the disc brake caliper assemblybeing actuated by pressurising the hydraulic fluid in the expansionchamber to move the piston relative to the caliper housing in an axialdirection such that the brake pads frictionally engage the rotary discbrake and such that the friction clutch surfaces become disengaged, thedistance moved by the piston being greater than the functional gapbetween the actuator nut and the thrust washer if wear of the brake padshas occurred such that the thrust washer engages the actuator nut torotate the actuator nut and the actuator means about the actuator screwrelative to the caliper housing and to move the actuator nut relative tothe caliper housing in the same axial direction as the piston, reverserotation of the actuator nut and the actuator means being prevented bythe reengagement of the friction clutch surfaces on release of thehydraulic fluid pressure thereby restricting reverse axial movement ofthe piston to a wear adjusted position relative to the caliper housing.

Preferably, the actuator means comprises an actuator cone in which thefriction clutch surface thereon is around the circumference of one endthereof and at an angle to the longitudinal axis of the piston, and thefriction clutch surface in the internal bore of the piston is at acorresponding angle. In this case, the angle of the friction clutchsurfaces is approximately 45 degrees plus or minus 15 degrees.

The resilient means can comprise an elastic washer.

Preferably, a bearing means is positioned between the resilient meansand the actuator means to permit rotation of the actuator means relativeto the piston on disengagement of the friction clutch surfaces. In thiscase, the thrust washer is preferably positioned between the bearingmeans and the actuator means and acts on the actuator means. The bearingmeans preferably comprises a ball bearing housing with a plurality ofball bearings housed therein.

The actuator nut preferably has an external portion having a shapedcross-section and the actuator means has an internal portion having acorrespondingly shaped cross-section, such that the external portionfits inside the internal portion to prevent the actuator nut rotatingrelative to the actuator means. In this case, the shaped external andinternal portions are preferably hexagonal in cross-section. The edgeportion of the actuator nut engageable by the thrust washer ispreferably defined by the external portion thereof.

Preferably, the actuator screw has an associated mechanism formechanical actuation of the disc brake caliper assembly.

The present invention will now be described, by way of example, withreference to the accompanying dr in which:

FIG. 1 is a cross-sectional view of a first embodiment of disc brakecaliper assembly in accordance with invention;

FIG. 2 is a cross-sectional view of a second embodiment of a disc brakecaliper assembly in accordance with invention;

FIG. 3 is a cross-sectional view of the piston, actuator nut, andactuator cone assembly of the disc brake caliper assembly shown in FIG.1;

FIG. 4 is a cross-sectional view of the caliper housing and the actuatorscrew and associated mechanism of the disc brake caliper assembly shownin FIG. 1;

FIG. 5 is a cross-sectional view of the caliper housing and the actuatorscrew and associated mechanism of the disc brake caliper assembly shownin FIG. 2;

FIGS. 6 and 7 are end and cross-sectional views respectively of theresilient clips shown in FIGS. 1 and 2;

FIG. 8 is an end view of the pistons shown in FIG. 3;

FIG. 9 is a cross-sectional view of the threads of the actuator nut andactuator screw of the disc brake caliper assemblies shown in FIGS. 1 and2;

FIG. 10 is a cross-sectional view on the line X--X of FIG. 3; and

FIG. 11 is a view similar to FIG. 3 of a third embodiment of the presentinvention.

Referring to FIG. 1 of the drawings, a disc brake caliper assembly 10 inaccordance with a first embodiment of the present invention is shown inposition about a portion of a rotary disc brake 12. The disc brakecaliper assembly 10 comprises a caliper housing 14 and inboard andoutboard brake shoes 16,18 respectively. Each brake shoe 16,18 has abrake pad 20,22 respectively of friction lining material forfrictionally engaging the rotary disc brake 12. A retainer spring 24secures the outboard brake shoe 18 to the caliper housing 14.

The inboard brake shoe 16 is secured by a resilient clip 26 to a piston28. The arrangement of the resilient clip 26 and the piston 28 is shownmore clearly in FIGS. 3, 6, 7 and 8. The resilient clip 26 has fourinwardly projecting legs 118 and four outwardly projecting legs 120(which are substantially U-shaped). The resilient clip 26 is secured tothe piston 28 by passing the inwardly projecting legs 118 throughcorresponding grooves 32 in one end 29 of the piston, and then rotatingthe resilient clip relative to the piston such that the inwardlyprojecting legs engage a lip 122 defined by an annular groove 124 in thepiston adjacent the said one end 29. The outwardly projecting legs 120engage and secure the inboard brake shoe 16 to the piston 28. Theinboard brake shoe 16 also has a lug 30 which into one of the grooves 32in the piston 28 to which provides the means to key the inboard brakeshoe and the piston together to prevent them rotating relative to oneanother.

The piston 28 is slidably mounted in, and projects from one end 33 of, acavity 34 in the caliper housing 14. The piston 28 and the caliperhousing 14 define an expansion chamber 36 in the cavity 34. An inletport (not shown) provides an inlet for hydraulic fluid to the expansionchamber 36. A piston seal 38 is positioned in a groove 40 in the wallsof the cavity 34 to provide a seal with the piston 28 to substantiallyprevent leakage of hydraulic fluid from the expansion chamber 36 aroundthe piston. A flexible boot 42 engages the piston 28 and the walls ofthe cavity 34 adjacent the end 33 of the cavity from which the pistonprojects. The flexible boot 42 substantially prevents dirt and moistureentering the cavity 34, thereby substantially preventing damage to thepiston seal 38 or to the walls of the cavity and/or the piston 28.Sealingly mounted in the caliper housing 14 is an actuator screw 44,which is secured to associated mechanism 45 (see FIG. 4), and whichpasses through an opening 46 at the opposite end 48 of the cavity 34.The associated mechanism 45 comprises a parking brake lever 50, a leverseal 52 (which is a moulded rubber seal with a resilient metallicinsert), a screw seal 54, a thrust washer 56, and a jam nut 58. Theactuator screw 44 has a shank which has a short external threadedportion 60 adjacent one end, a long external threaded portion 62adjacent the other end, and an intermediate stepped portion 64. Theactuator screw 44 and associated mechanism 45 are assembled as shownwith the jam nut 58 threaded to the short external threaded portion 60of the shank of the actuator screw. A portion of the intermediatestepped portion 64 is rotatably mounted in the opening 46. The screwseal 54 is positioned in a groove 63 in the intermediate stepped portion64 and engages the wall of the opening 46 to substantially preventleakage of hydraulic fluid from the expansion chamber 36 around theintermediate stepped portion 64 of the actuator screw 44. The thrustwasher 56, lever seal 52 and jam nut 58 secure the actuator screw 44 inposition, but allow rotation thereof about its longitudinal axis Arelative to the caliper housing 14. The parking brake lever 50 isattached to the intermediate stepped portion 64 of the actuator screw 44in such a way that the parking brake lever and the actuator screw rotatetogether about the axis A. The long external threaded portion 62 of theactuator screw 44 projects into an internal bore 65 having an open end67 (FIG. 3) formed in the piston 28 at the opposite end to the said oneend 29.

An actuator nut 66 threadingly engages (by threads 61) the long externalthreaded portion 62 of the actuator screw 44 within the internal bore 65of the piston 28. The actuator nut 66 has a first small diameter portionand a second large diameter portion with a circumferential edgetherebetween. The actuator nut 66, actuator screw 44, and internal bore65 all have the same longitudinal axis A. In the embodiment of FIG. 1,and as shown in more detail in FIG. 3, the actuator nut 66 is attachedto the piston 28 by actuator means 68.

The actuator means 68 comprises an actuator cone 69; thrust washers70,71; bearing means 72 comprising a ball bearing housing 73 and aplurality of ball bearings 74; an elastic washer (resilient means) 75;and a retainer 76 which is ring-shaped. As seen in FIG. 3, the retainer76 is positioned in, and secured to, the internal bore 65 of the piston28 adjacent the open end 67 of the piston. The elastic washer 75 ispositioned between, and engages, the retainer 76 and one of the thrustwashers 71. The bearing means 72 is positioned between, and engages, thethrust washers 70,71. The other thrust washer 70 engages one end 77 ofthe actuator cone 69. The other end 78 of the actuator cone 69 isdirected towards the one (or closed) end 29 of the piston 28. Anexternal portion 79 of the actuator nut 66 has a hexagonal cross-section(FIG. 10) which corresponds to an internal portion 80 of the actuatorcone 69 having a similar cross-section. This arrangement is such thatrelative rotation about axis A between the actuator nut 66 and theactuator cone 69 is substantially prevented.

The external portion 79 of the actuator nut 66 has a number oflongitudinally extending grooves 81 in its outer surface, and actuatorcone 69 has a through aperture 82. The grooves 81 and the aperture 82ensure hydraulic fluid completely fills the expansion chamber 36.

A circumferentially extending portion of the other end 78 of theactuator cone 69 defines a friction clutch surface 83 which frictionallyengages a corresponding surface 84 on the internal bore 65 of the piston28. In this particular embodiment, the friction clutch surfaces 83,84are at approximately 45 degrees to the axis A, although any suitableangle may be used.

When the brake is not in use, the elastic washer 75 acts through thethrust washers 70,71 and the bearing means 72 on the actuator cone 69 toretain the friction clutch surfaces 83,84 in engagement. Also, theactuator nut 66 is retained within the internal bore 65 such that whenthe brakes are not applied, a functional gap F exists between an edgeportion 85 of the external portion 79 of the actuator nut and the thrustwasher 70, and a functional gap H exists between the actuator nut and anabutment surface 86 on the actuator cone 69 as shown in FIG. 3.Similarly, a functional gap G exists between the threads 61 of theactuator nut 66, and the threads of the longitudinally extending portion62 of the actuator screw 44 as shown in FIG. 9.

The hydraulic and mechanical actuation of the disc brake caliperassembly 10 of FIG. 1 will now be described in more detail.

Hydraulic actuation is achieved by the vehicle operator applying thebrakes in the usual way, for example, by depression of the vehicle brakepedal (not shown). Hydraulic fluid passes through the inlet port (notshown) into the expansion chamber 36. The build up of pressure in theexpansion chamber 36 forces the piston 28 to move in the axial directionX relative to the caliper housing 14. This movement of the piston 28moves the brake pad 20 on the inboard brake shoe 16 into frictionalengagement with the rotary disc brake 12, and by a reaction forcethrough the caliper housing 14 similarly moves the brake pad 22 of theoutboard brake shoe 18 into frictional engagement with the rotary discbrake. As soon as the piston 28 moves, the elastic washer 75 iscompressed and the friction clutch surfaces 83, 84 become disengaged.The actuator cone 69 is equally hydraulically pressed on all itssurfaces. When the vehicle operator releases the brakes, the pressure inthe expansion chamber 36 is released and the elastic reaction force ofthe piston seal 38 moves the piston 28 back in the opposite direction toX.

If wear of the brake pads 20,22 does not occur, the piston 28 moves inthe axial direction X a distance which is less than or equal to the sumof the functional gaps F and G, and the thrust washer 70 does not engageand move the actuator nut 66. That is, the position of the actuator nut66 relative to the caliper housing 14 does not change during hydraulicapplication of the brakes. If wear does occur, the piston 28, moves adistance which is greater than the sum of the functional gaps F and G,causing the thrust washer 70 to engage the edge portion 85 of theactuator nut 66, which causes the actuator nut to rotate about theactuator screw 44 and also move in the axial direction X relative to thecaliper housing 14.

With the friction clutch surfaces 83,84 out of engagement, the actuatorcone 69 is also free to rotate about the actuator screw 44 relative tothe piston 28. Such rotation is caused by the rotation of the actuatornut 66 due to the hexagonal cross-sections of the external and internalportions 79,80 respectively of the actuator nut 66 and the actuator cone69 respectively, and is permitted due to the presence of the bearingmeans 72. When the hydraulic pressure is released, the friction clutchsurfaces 83,84 are or become reengaged due to the action of the elasticwasher 75 on the actuator cone 69, thereby preventing reverse rotationof the actuator cone 69 and the actuator nut 66 relative to the actuatorscrew 44, and thereby preventing movement of the actuator nut in adirection opposite to X. Because the piston 28 is keyed to the inboardbrake shoe 16 by the lug 30 and groove 32 arrangement, the piston isprevented from rotating about the actuator screw 44, and as aconsequence, the piston can only move in the direction opposite to X(assisted by the elastic reaction force of the piston seal 38) by adistance which is sufficient to restore the functional gaps F and Gbetween the actuator nut 66 and the thrust washer 70, and the screwthreads 61,62, that is, the piston moves back to a new (wear adjusted)position relative to the caliper housing. This arrangement thereforeprovides automatic adjustment for wear each time the brakes arehydraulically applied.

The disc brake caliper assembly 10 is actuated mechanically by thevehicle operator in the usual way, for example, by actuation of the handbrake lever (not shown). Such actuation results in a force being appliedto the parking brake lever 50, causing the parking brake lever and theactuator screw 44 to rotate about the axis A relative to the caliperhousing 14. The force exerted by the elastic washer 75 on the actuatorcone 69 keeps the friction clutch surfaces 83,84 in engagement. Thisprevents rotation of the actuator cone 69, and hence the actuator nut66, about the axis A in the same direction as the actuator screw 44, andthe lug 30 and groove 32 arrangement prevents the piston 28 rotatingwith the actuator screw 44. As a consequence the actuator nut 66 movesin the axial direction X relative to the caliper housing 14 to close thefunctional gap H, engage the abutment surface 86, and move the piston 28in the axial direction X. Such movement of the piston 28 moves the brakepad 20 of inboard brake shoe 16 into frictional engagement with therotary disc brake 12, and, by a reaction force through the caliperhousing 14, similarly moves the brake pad 22 of the outboard brake shoe18 into frictional engagement with the rotary disc brake.

Release of the mechanical actuation reverses the direction of rotationof the parking brake lever 50 and actuator screw 44 about the axis Arelative to the caliper housing 14. This causes the actuator nut 66 andthe actuator cone 69 (and the piston 28) to move axially in a directionopposite to X relative to the caliper housing 14 because the engagementof the friction clutch surfaces 83, 84 prevents the actuator nut and theactuator cone rotating relative to the actuator screw 44 during thisreverse axial movement. The elastic reaction force of the piston seal 38also assists in moving the piston 28 back to its original position. Innormal conditions (which include a range of pressure actuations), nowear adjustment occurs during mechanical actuation.

A second embodiment of disc brake caliper assembly 10' in accordancewith the present invention is shown in FIG. 2. This second embodiment issimilar to the first embodiment shown in FIG. 1, and similar parts havebeen given the same reference number. The main difference between thesecond embodiment and the first embodiment is the actuator screw, itsassociated mechanism, and its mode of operation. The caliper housing 14'of this third embodiment has been modified to accommodate the abovementioned differences. The caliper housing 14' includes a channelsection 88 extending from the opening 46 at its opposite end 48. Theactuator screw 90 in FIG. 2 comprises a shank 91 having an externalthreaded portion 92 and a head 94. The external threaded portion 92threadingly engages the threads 61 of the actuator nut 66. Theassociated mechanism 96 (see FIG. 5) comprises a parking brake lever 98,an eccentric shaft 99, a pushrod 100, a piston member 102, a seal 104, awasher 106, a spring 108, a spring retainer 110, a thrust washer 112 anda retainer stop 114. The piston member 102 is a sliding fit in thechannel section 88 of the caliper housing 14' and has a groove 116therein in which the seal 104 is positioned to substantially preventleakage of hydraulic fluid from the expansion chamber 36 around thepiston member. The piston member 102 is secured at one end to the head94 of the actuator screw 90, and engages the pushrod 100 at its otherend. The pushrod 100 also engages the eccentric shaft 99, which isconnected to the parking brake lever 98. This arrangement is such thatif the parking brake lever 98 is rotated about the longitudinal axis Bof the actuator screw 90, the eccentric shaft 99 is also rotated causingthe pushrod 100, the piston member 102 and the actuator screw 90 to movein an axial direction (parallel to the axial direction X) along the axisB. This arrangement differs from that in the first embodiment of FIG. 1,where rotation of the parking brake lever 50 causes rotation of theactuator screw 44 about its longitudinal axis A. In this secondembodiment, rotation of the parking brake lever 98 causes axial movementof the actuator screw 90 along its longitudinal axis B relative to thecaliper housing 14'. The spring 108 and its spring retainer 110 andthrust washer 112 are positioned on the opposite side of the head 94 ofthe actuator screw 90 to the piston member 102 within the expansionchamber 36.

The hydraulic and mechanical actuation of this second embodiment of discbrake caliper assembly 10' will now be described.

The hydraulic actuation of the second embodiment of FIG. 2 is the sameas that of the first embodiment of FIG. 1.

The disc brake caliper assembly 10' is operated mechanically in theusual way by the vehicle operator, for example, by actuation of the handbrake lever (not shown). Such actuation results in a force being appliedto the parking brake lever 98 which rotates the parking brake lever andthe eccentric shaft 99 about the axis B relative to the caliper housing14'. Rotation of the eccentric shaft 99 causes the pushrod 100, thepiston member 102 and the actuator screw 90 to move in the axialdirection X relative to the caliper housing 14'. As the head 94 of theactuator screw 90 engages the thrust washer 112, the thrust washer 112is also moved in the axial direction X relative to the caliper housing14'. A flat(s) (not shown) on the interior of washer 106 abuts a flat(s)(not shown) of the head 94 to prevent rotation the actuator screw 90. Asthe spring retainer 110 engages the retainer stop 114, the spring 108 iscompressed due to the relative movement of the thrust washer 112. Theforce exerted by the elastic washer 75 on the actuator cone 69 keeps thefriction clutch surfaces 83,84 in engagement. This prevents rotation ofthe actuator cone 69, and hence the actuator nut 66, about the axis B inthe same direction as the actuator screw 90, and the lug 30 and groove32 arrangement prevents the piston 28 from rotating relative to thecaliper housing 14'. As a consequence, the axial movement of theactuator screw 90 causes the actuator nut 66 to move in the axialdirection X relative to the caliper housing 14' to close the functionalgap H. The actuator nut 66 then engages the abutment surface 86 of theactuator cone 69 to move the piston in the axial direction X relative tothe caliper housing 14'. Such movement of the piston 28 moves the brakepad 20 of inboard brake shoe 16 into frictional engagement with therotary disc brake 12, and, by a reaction force through the caliperhousing 14', similarly moves the brake pad 22 of the outboard brake shoe18 into frictional engagement with the rotary disc brake.

Release of the mechanical actuation reverses the direction of rotationof the parking brake lever 98 and eccentric shaft 99 about the axis Brelative to the caliper housing 14'. This allows the pushrod 100, thepiston member 102, and the actuator screw 90 to move axially in thereverse direction to X relative to the caliper housing 14' under theaction of the spring 108. The engagement of the friction clutch surfaces83, 84 prevents the actuator nut 66 and actuator cone 69 rotatingrelative to the actuator screw 90 during this reverse axial movement.The actuator nut 66, actuator cone 69 and the piston 28 therefore alsomove axially in a reverse direction to X relative to the caliper housing14'. The elastic reaction force of the piston seal 38 also assists inmoving the piston 28 back to its original position, and no wearadjustment occurs.

In FIG. 11 a third embodiment of the present invention has the thrustwasher 70 directly load the actuator 366. Therefore, the prior gapping Fis eliminated and actuator cone 369 is continually urged towards theinboard shoe 16 by contact with the actuator nut 66. With the abovearrangement the functional gap is equal the gap G and adjustment willoccur whenever wear on the shoe linings exceed the gap G.

A particular advantage provided by the embodiment of FIG. 11 is that theangular rotation of the parking brake lever 50 required for mechanicalactuation is lowered as compared with the embodiment of FIG. 1 becauseof the elimination of gaps F and H. Additionally, the embodiment of FIG.11 utilizes a metallic spring wave-type washer 375 as a resilient means,located by a cone type retainer 376. The actuator cone 369 has a seriesof slots 399 to allow free flow of hydraulic fluid in front of the cone369.

An advantage of the present invention is that on a hydraulic apply thehydraulic line pressure creates a force that causes the piston 28 toload the inboard shoe 16 and the housing 14 to load the outboard shoe18. As the piston moves out against the shoe the actuator cone 69,369 isunloaded from the piston 28,29. The only load on the actuator cone69,369 is the low force from the resilient means. As the piston 28,29and actuator cone 69,369 separate the spring load builds up on theactuator cone 69,369 to follow the piston 28. Upon release, the piston28,29 retracts due to two forces, the caliper housing 14 and shoe andlining deflection forces and the piston seal 38 retraction force. Thepiston retraction is limited by the functional gap and the load - travelrelationship of the resilient means.

The piston 28,29 is adjusted on apply and the piston retraction iscontrolled by the retraction forces functional gap and by the loadtravel relationship of the resilient means. The above, therefore, allowsfor optimization of the opposing desires of low mechanical travel andlow residual load by varying the parameters of functional gap and orload travel relationship of the compliance means.

On a mechanical apply the input torque and rotation of the screw (oraxial movement) creates a force that causes the piston 28,29 to load theinboard shoe 16 and the housing 14 to load the outboard shoe 18. Theactuator screw thread drives the actuator nut which drives the piston 28through the actuator cone 69,369.

Upon a mechanical release the piston 28,29 is retracted not only by theseal 38 retraction forces but also caliper 10 deflection forces. Theopposing force is the resilient means and the thread friction. Untilthese forces are balanced the piston 28,29 will still retract as theactuator nut 66,366 moves axially back as the actuator screw 44 isrotated back. The nut 66,366 does not rotate due to the loading of thecone 69,369 and piston 28,29 by the caliper deflection forces. Theaforementioned allows optimization of the opposing desires of lowmechanical travel and low residual load by varying the parameters of theresilient means controlling the load, rate, and deflection.

Various alterations could be made to the above described arrangementswithout departing from the scope of the present invention. For example,the external and internals portions 79,80 respectively could have ashape other than hexagonal, but be of such a shape as to preventrelative rotation of the actuator nut 66 relative to the actuator cone69. Further, the actuator nut 66 has been shown as a male component, andthe actuator cone 69 as a female component; but the opposite arrangementwill equally work. Further still, the actuator cone 69 could be replacedby cylindrical sleeve, one end of which defines a friction clutchsurface which engages a friction clutch surface on the piston 28,29which is substantially normal to the axis A. Further still, the elasticwasher could be replaced by a spring or any other suitable form ofresilient means. Any suitable form of bearing means may be used otherthan ball bearings.

Although the present invention has been described in relation tofloating disc brake caliper assemblies, it could equally apply to anyform of disc brake caliper assembly. Similarly, although the presentinvention has been described in relation to disc brake caliperassemblies having a parking (mechanically operated) brake, it couldequally apply to disc brake caliper assemblies without a parking brakeas long as an actuator screw is present within the internal bore of thepiston.

The present invention has the advantages of providing wear adjustmentduring hydraulic actuation of the brake which substantially correspondsto the wear on the brake pads, and of providing a relatively cheap andsimple arrangement for providing such wear adjustment.

We claim:
 1. A disc brake caliper assembly for a rotary disc brake of avehicle comprising first and second brake shoes having integral brakepads of friction lining material for frictionally engaging oppositesides of the rotary disc brake; a caliper housing having a cavitytherein defining an expansion chamber for hydraulic fluid; an inlet portopening into the expansion chamber for passage of the hydraulic fluid; apiston sealingly slidably mounted in the cavity in the caliper housingand projecting from one end of the cavity, the first brake shoe beingsecured to the piston at one end thereof outside the cavity with meansto key the first brake shoe and the piston together to prevent thepiston rotating relative to the caliper housing, the piston having aninternal bore having a longitudinal axis and having an open end openinginto the expansion chamber; a thrust washer secured in the internal boreof the piston; an actuator nut positioned in the internal bore with afirst smaller diameter and a second larger diameter, and with afunctional gap between a circumferential edge portion of the actuatornut between the first smaller and the second larger diameters and thethrust washer, the actuator nut having a longitudinal axis; and anactuator screw mounted in the cavity in the caliper housing andprojecting from the other end of the cavity, the actuator screw having alongitudinal axis, the longitudinal axes of the actuator screw, theactuator nut, and the internal bore being aligned, the actuator screwextending into the internal bore and threadingly engaging the actuatornut; and actuator means positioned in the internal bore of the pistonand engaging the actuator nut along the larger diameter portion, theactuator means having a friction clutch surface normally resilientlybiased by resilient means into engagement with a corresponding frictionclutch surface in the internal bore of the piston and directed towardsthe open end thereof, being rotatable relative to the piston ondisengagement of the friction clutch surfaces, and being rotatably fixedrelative to the actuator nut but axially movable relative thereto;hydraulic actuation of the disc brake caliper assembly being actuated bypressurising the hydraulic fluid in the expansion chamber to move thepiston relative to the caliper housing in an axial direction such thatthe brake pads frictionally engage the rotary disc brake and such thatthe friction clutch surfaces become disengaged, the distance moved bythe piston being greater than the functional gap between the actuatornut and the thrust washer if wear of the brake pads has occurred suchthat the thrust washer engages the actuator nut circumferential edgeportion to rotate the actuator nut and the actuator means about theactuator screw relative to the caliper housing and to move the actuatornut relative to the caliper housing in the same axial direction as thepiston, reverse rotation of the actuator nut and the actuator meansbeing prevented by reengagement of the friction clutch surfaces onrelease of the hydraulic fluid pressure thereby restricting reverseaxial movement of the piston to a wear adjusted position relative to thecaliper housing.
 2. A disc brake caliper assembly as claimed in claim 1,wherein the actuator means comprises an actuator cone in which thefriction clutch surface thereon is around the circumference of one endthereof and at an angle to the longitudinal axis of the piston, and thefriction clutch surface in the internal bore of the piston is at acorresponding angle.
 3. A disc brake caliper assembly as claimed inclaim 2, wherein the angle of the friction clutch surfaces isapproximately 45 degrees.
 4. A disc brake caliper assembly as claimed inclaim 1, wherein the resilient means comprises an elastic washer.
 5. Adisc brake caliper assembly as claimed in claim 1, wherein the resilientmeans comprises a metallic spring washer.
 6. A disc brake caliperassembly as claimed in claim 1, wherein a bearing means is positionedbetween the resilient means and the actuator means to aid rotation ofthe actuator means relative to the piston on disengagement of thefriction clutch surfaces.
 7. A disc brake caliper assembly as claimed inclaim 6, wherein the thrust washer is positioned between the bearingmeans and the actuator means and acts on the actuator means.
 8. A discbrake caliper assembly as claimed in claim 6, wherein the bearing meanscomprises a ball bearing housing with a plurality of ball bearingshoused therein.
 9. A disc brake caliper assembly as claimed in claim 1,wherein the actuator nut has an external portion having a shapedcross-section and the actuator means has an internal portion having acorrespondingly shaped cross-section, such that the external portionfits inside the internal portion to prevent the actuator nut rotatingrelative to the actuator means.
 10. A disc brake caliper assembly asclaimed in claim 9, wherein the shaped external and internal portionsare hexagonal in cross-section.
 11. A disc brake caliper assembly asclaimed in claim 9, wherein the external portion of the actuator nutdefines the edge portion thereof engageable by the thrust washer.
 12. Adisc brake caliper assembly as claimed in claim 1, wherein the actuatorscrew has an associated mechanism for mechanical actuation of the discbrake caliper assembly.
 13. A disc brake caliper assembly as claimed inclaim 12, wherein the actuator screw is rotated by the associatedmechanism to mechanically actuate the disc brake assembly.
 14. A discbrake caliper assembly as claimed in claim 12, wherein the actuatorscrew is moved axially by the associated mechanics to mechanicallyactuate the disc brake assembly.
 15. A disc brake caliper assembly asdescribed in claim 1, wherein the means to keep the first brake shoe andthe piston together includes the first brake shoe having a lugprotecting therefrom on the opposite side to the brake pad and the lugprojects into a corresponding groove in the piston.